1. Field of the Invention
This invention relates to improvements in near infrared measuring instruments, and particularly such instruments that are utilized for measuring constituents, such as protein, moisture and oil in materials using near infrared radiation on a nondestructive basis.
2. Description of the Background Art
Near infrared measuring instruments that provide an accurate measure of constituents, such as protein, moisture and oil in grain and other products utilizing near infrared radiation are known in the art and have become commercially successful. Such instruments are particularly useful for measuring protein, oil and moisture in cereal grain in a totally nondestructive mode to a high degree of accuracy and with superior speed. Such instruments are commercially available from Trebor Industries, Inc. in Gaithersburg, Maryland, and are sold for example under the trademark TREBOR-90 and are disclosed in U.S. Pat. Nos. 4,286,327 and 4,404,642, inter alia.
These known instruments have proven to be commercially successful. Nevertheless, even though commercially successful they do have certain limitations. One of the most important of these limitations results from the fact that different types of grain and other materials have grossly different optical characteristics. For example, a fifteen millimeter cross-section of wheat has an optical density of between 4 and 5 (optical density is defined as the log (1/T) where T is the fraction of light transmitted through the sample). A fifteen millimeter cross-section of corn has much less optical density (i.e., it is much more transparent). Sunflower seeds have an optical density much greater than wheat and are practically optically opaque in an instrument with a fifteen millimeter cross-section. Rape seed are similar to sunflower seeds with regard to optical density.
To at least partially overcome the limitation due to the different optical densities of different grains, the TREBOR commercial instruments include in their instrumentation dual electronic gain to allow the same instrument to measure two different types of grain, for example, corn as well as wheat. However, the use of dual electronic gain does not work well on materials that are more optically opaque and therefore TREBOR manufactures separate instruments with a much smaller cross section thickness for sunflower seed and rape seed as well as for other cereal grains such as millet, etc. This need for separate instruments or different circuits in the same instrument for different types of grains hinders the usefulness, versatility and marketability of the instruments because most grain elevators handle a wide variety of grain and would prefer to utilize a single instrument for any grain they handle.
A further limitation with the existing commercial products is that the ejection wheel system for grain does not operate well on all types of grain. An ejection wheel works extremely well on wheat, barley, corn, soy bean and milo and on other grain products where the grain kernels are essentially solid in nature. However, it has been recently discovered that on long-grain rice, i.e., rice that has a very long "tail", the ejection wheel begins to jam. Although this is not a major limitation, it does cause concern and does limit the usefulness and versatility of the instrument.
Further, in the known prior art instruments, measurements of grain must be taken after the grain has stopped moving. The time it takes for the grain to stop moving varies with the wetness, temperature and random orientation of the grains. The prior art instruments have had to be adapted to accommodate the maximum time of grain movement and thus have built-in inefficiencies timewise. In other words, the ejection wheel which moves the grain must be able to move the grain independent of the moisture and temperature level of the grain, but the grain must stop moving in order to take an accurate measurement. As the ejection wheel gets older and wears or as damage occurs, such wheels need to be replaced causing undesirable "down time".
The limitations of the prior art ejection wheel type of instruments have also made them unsuitable for measuring constituents present in materials such as flours, meals, liquids, pastes and the like.
These problems and limitations with the known prior art have existed for the years since the Trebor instruments have been on the market with no overall satisfactory solution even though there has been an incentive to overcome such limitations.